Grouping error in ext-4.2.1.883

Hi,

Step to replicate:

1. create a grid with groupings.
2. filter the grid until it only has one group shown.
3. click on any row within the group and click another row (this works fine... browser does not hang).
4. filter the grid until it shows two or more groups.
5. click on any row and the browser hangs.

Note that there is no itemclick or itemdblclick event yet on the gridpanel or viewpanel.

When I remove the Grouping Feature, there's no problem when rows are clicked.

Some more inputs:
1. In the Store, I configured groupField to a particular Field (customer_name).
2. On apps startup, the grid shows more than two groupings (per customer).
3. This is when the browser hangs-up if you click on a row.

4. But when I started working on the grouping before clicking any row, there's no problem, such as:
4.a. group the data based on another column/field.
4.b. apply grid filter until only 1 customer group shows in the grid.

The reason I specified a "groupField" in the store is to have the data pre-grouped by customer once the application loads. Is there any other way to do it?